1. Field of the Invention
The present invention relates to semiconductor packaging and, more particularly, to an underfill system for a semiconductor package that prevents voids or bubbles within a gap between a semiconductor chip and a substrate during an underfill process and which shortens the underfill time.
2. Description of the Related Arts
There are many bonding techniques for semiconductor devices, i.e., wire bonding, tape automated bonding (TAB), flip chip bonding, anisotropic conductive film (ACF) bonding, etc. Recent trends in electronics development are towards light weight, miniaturization, high speed, multi-functionalization, high quality, high reliability and so on. In order to satisfy these demands, the flip chip bonding technique has been introduced and widely employed.
The flip-chip bonding technique involves mounting a semiconductor chip onto a substrate through bonding bumps formed on the electrode pads of the semiconductor chip. Solder bumps, Au bumps or stud bumps are used. Solder bumps and Au bumps are formed by a plating method, while stud bumps are formed by a wire-bonding method.
After flip-chip bonding the semiconductor chip to the substrate, in order to prevent failures due to differences in thermal expansion coefficients of the semiconductor chip and the substrate, an underfill process for filling the gap between the semiconductor chip and the substrate with a filling material is performed. FIG. 1 is a cross-sectional view of a portion of a semiconductor package, where a gap between a semiconductor chip and a substrate is filled by the prior art underfill method.
As shown in FIG. 1, a dispensing method is conventionally used as the underfill method. After flip chip bonding bumps 14 attach a surface of a semiconductor chip 12 to a substrate 10, the gap between the semiconductor chip 12 and the substrate 10 is filled by injecting a liquid filling material 18 with a dispenser 16. Reference number 19 represents a piston 19 for injecting the filling material 18 into the gap.
In the above-described dispensing method, the filling speed of the filling material 18 is determined by surface tension between the semiconductor chip 12 and the substrate 10. The consequent long filling time of the filling material 18 and high number of bumps 14 cause voids or air bubbles to form within the gap.
In order to solve this problem, the filling speed of the filling material should be increased by supplying injection pressure or by performing the filling under vacuum conditions.
However, in case of supplying injection pressure so as to fill the gap with the filling material, the bumps may deviate from their earlier original positions by the filling speed of the filling material.
In case of supplying a vacuum condition, as disclosed in U.S. Pat. No. 5,866,442, an underfill apparatus using a vacuum condition requires additional equipment such as a pressure pump and a vacuum pump, thereby increasing the fabrication cost. Furthermore, since this apparatus cannot simultaneously carry out the underfill process to a plurality of the substrates, it reduces the production yield.